The escalating requirements for high-density and performance associated with ultra large scale integration (ULSI) semiconductor devices require responsive changes in interconnection technology. Low dielectric constant (“low-k”) interlevel dielectric (ILD) materials have been found effective in mitigating RC (resistance capacitance) propagation delays to reduce power consumption and crosstalk. Materials which show promise as low-k dielectric materials include various carbon-containing materials. Such carbon-containing low-k dielectric materials include various polymers with carbon occupying a position in the backbone of the polymer. Typical of such carbon-containing polymers are benzocyclobutene (BCB), methyl silsesquioxane (MSQ), Flare-R®, Silk®, Orion, JSR and Black Diamond®. Although materials having a dielectric constant of less than about 3.9 are considered low-k dielectric materials, as integrated circuit devices and interconnect technologies continue to scale smaller, low-k dielectric materials with even lower dielectric constants have become useful, and it is increasingly popular to use materials having dielectric constants less than or equal to 3, i.e., k≦3. The challenges posed by the increasingly fragile and higher carbon content of the k≦3 materials impact plasma technology used in the manufacture of semiconductor devices because the Si—CH3, Si—C and other carbon bonds in the low-k dielectric material are susceptible to attack by the plasma processing. More particularly, the oxygen plasmas typically used to strip the organic photoresist layers formed over the low-k dielectric materials, may penetrate the low-k dielectric material and complex with the carbon in the low-k dielectric material. Plasma excitation during the stripping process results in atomic oxygen that combines with carbon from the low-k dielectric material and causes the carbon to leach out of the film, undesirably increasing the dielectric constant of the film.
As such, there have been attempts to strip photoresist using oxygen-free plasmas. One attempt to strip photoresist in an oxygen-deficient environment is provided in U.S. Pat. No. 6,030,901 issued on Feb. 29, 2000 to Hopper, et al, entitled Photoresist Stripping Without Degrading Low Dielectric Constant Materials. U.S. Pat. No. 6,235,453, issued May 22, 2001 to You, et al, entitled Low-k Photoresist Removal Process, teaches a photoresist removal process that uses a trace amount of O2. Such attempts have generally been unsuccessful because of low stripping rates and polymer build-up in the plasma chamber. The oxygen in conventional plasmas typically complexes with the organic photoresist to produce gases such as CO2, CO, and H2O, which are easily pumped out of the plasma chamber. Due to the lack or only trace amount of oxygen, each of the aforementioned references include the shortcomings of a low strip rate due to the lessened reactivity toward the photoresist, and polymer build-up in the etch chamber due to the lack of liberation of easily removable gases such as CO, CO2 or H2O. Furthermore, such oxygen-deficient plasmas lack the ability to strip polymeric by-products or penetrate the hard skin which forms on photoresist layers during aggressive etch processes such as the via etch in a via first process sequence or other damascene technology etches.
It would therefore be desirable to provide a method for manufacturing a semiconductor device that overcomes the above-described shortcomings and provides a photoresist stripping process that does not degrade low-k dielectric material.